I. Field of the Invention
The process and apparatus of this invention, and the bodies produced thereby relate generally to the field of molded plastic or resin bodies for commercial and industrial uses where heretofore other structural materials like wood or metals were used. The invention also relates to the use of reduced pressure systems to form polyurethane bodies and other solid polymer bodies.
II. Description of the Prior Art
It is known to form molded plastic bodies by means of equipment which pours or presses the liquid resin into a mold so as to form, for example, a solid polyurethane body. The bodies produced by such a procedure contain some entrapped air bubbles or gas bubbles as the result of the reaction of entrapped moisture with the reactants, however, and have disadvantageous physical characteristics for some applications. The requirements of structural engineering plastics are such that no air or bubbles, even in the form of microbubbles, should be found in the solid body.
In my U.S. Pat. No. 4,016,130 entitled "Production of Solid, Rigid Filled Polyurethane Composites," I have devised a method for the formation of filled polyurethane bodies, which method uses a vacuum system in some of the steps. However, a vacuum was not applied to the mixture of ingredients during the mixing procedure in the method of that patent. The importance of avoiding bubbles of any type even at a molecular level, is becoming more apparent for producing polymer bodies of enhanced physical characteristics which heretofore were only available in other materials.
Other attempts to form resin bodies with enhanced characteristics are also known in the art. For example, Suter in the German Offenlegungsschrift No. 2,636,902 shows an injection molding system which uses a vacuum for degasifying, temporarily, the reactants prior to injecting them into a mold. However, that apparatus and method has shortcomings in the injection and transfer of the reactants where bubbles of both microscopic and macroscopic size are induced into the system thereby weakening the resultant bodies. Especially disadvantageous in that procedure is the use of screw pumps to feed the mixtures along lines to the molds. Suter is primarily directed toward the use of epoxy resins for electrical insulators.
Wikolin in Offenlegungsschrift No. 2,419,961 discloses a method for cyclically pressure injecting polyurethane into molds. Wikolin uses a vacuum after the reactants have been poured into the mold so as to assure the proper amount of reactants within a given batch of flowable plastic by preventing further flow of reactants into the mixing chamber. Notably, Wikolin does not apply a vacuum to the reactants prior to injection into the mold and this necessarily allows a significant portion of moisture and air to enter the mold and thereby detract from the physical characteristics of the bodies eventually produced.
Industrial and commercial applications demand that improved physical, mechanical, and other characteristics be obtained for solid, rigid polyurethane bodies and the like, both filled and unfilled, in order to use such bodies to replace what has heretofore been constructed from other structural materials. In order to achieve these characteristics, moisture and air must be eliminated as completely as possible from the reactants and mixture in order to achieve enhanced characteristics for the bodies subsequently formed in the molds.
Solid elastomer polyurethane bodies are normally somewhat translucent or milky as compared to a good transparent glass. This translucent characteristic of elastomers is attributable to, among other things, "voids" in the structure. Each bubble (void) whether microscopic or larger causes a mechanical weakness in the polyurethane body. It is necessary to eliminate all entrapped gases and moisture in order to prevent formation of such voids and form stronger molded pieces.